Im going to assume you have no experience with nitrous systems and say this up front, do not assemble your own custom kit with mis-matched parts your first time around.
Nextly an excellent performer on the SOHC 4.6 GT is Holley-NOS's "NOSzle" kit. The kit has simple installation for first time nitrous users and has the ability to grow with your car. The system comes with pills to run a 100hp or 125hp. If you decide you wanted to build your engine for even more nitrous the system is capable of delivering up to 300hp all by itself. The system injects nitrous and fuel in the same location as your fuel injectors making installation easy and maximizing combustion of the fed nitrous thus giving you more power. Because the kit is "wet" it injects more fuel ontop of what your fuel injectors already provide giving you alot more torque output and safer operation. I beleave this kit is a good option for you due to its simple install, safe operation and will give you more power to the ground than others. A stock GT with using this system set up for 150hp shot created 383HP and 505TQ at the wheels adding 149HP and over 200FT/TQ!!!!!